The causes of bubble formation

1. The unreasonable proportion of concrete results in high viscosity and difficult discharge of bubbles due to the use of many cementitious materials. Adding fly ash or mineral powder can be used to solve this problem or increase the water consumption.

2. The problem with cement itself is that grinding aids are added to cement during grinding, and some grinding aids have many bubbles.

3. The concrete vibration is uneven and the vibration time is not enough. During the concrete vibration process, air is easily mixed in, causing bubbles in the concrete mixture to not overflow inside.

4. The problem with the demoulding machine is that choosing a wrong demoulding machine may also cause bubbles to be difficult to discharge.

5. Excessive coarse aggregate and insufficient fine aggregate, or poor particle size and low sand content, resulting in the inability of fine aggregate to fill the pores of coarse aggregate and form bubbles.

Methods for eliminating bubbles

1. It is recommended to prioritize the use of cement with fewer bubbles and low alkali content. Control the quality of raw materials and eliminate unqualified materials.

2. Choose a reasonable gradation to ensure a moderate ratio of coarse and fine aggregates.

3. Choosing an appropriate water cement ratio can allow for multiple groups to be made in the laboratory and compared to select the best one. On the premise of ensuring the strength of concrete, it is recommended to use cement with lower grades or smaller deviations in relevant physical and technical performance indicators to increase the cement dosage.

4. Strive to reduce the deviation between actual production and experimentation. During the construction process, timely moisture content testing of materials should be carried out, and each vehicle of aggregate should be weighed. If electronic metering can be used, the effect will be better. Quality ratio control should be adopted, and on-site mix proportions should be adjusted at any time to avoid significant deviations in water usage and sand ratio.

5. Select high-quality chemical additives and cement. At present, there are many brands in this area, and it cannot be generalized. Conducting chemical analysis is certainly a method, but for actual production, the simplest and easiest way is to make several sets of test pieces and select a better one for production.

6. Pay attention to the mixing time, so that the admixture can be fully and evenly mixed with other raw materials. There are also standard requirements for mixing time. According to "7.5.2" of the "Ready Mix Concrete" GB/T14902, the mixing time for each plate during mixing production (calculated from the completion of all materials) should not be less than 30 seconds. When preparing concrete with a strength grade of C50 or above or using air entraining agents, expansion agents, and waterproofing agents, the mixing time should be increased. "

7. It is recommended that the construction unit pay attention to the vibration process. During the construction of concrete, it should be layered and vibrated layer by layer. The thickness of the layering should not exceed 50 cm, otherwise bubbles are not easily expelled from the inside of the concrete. Strictly follow the operation method of "fast insertion and slow extraction" for vibration operation, to prevent under vibration, missed vibration, and over vibration of concrete.

8. The template should be kept smooth, and the release agent should be applied evenly but not too much or too thick.

Bubble expansion information

The formation of bubbles mainly belongs to a physical cause. According to the principle of dense aggregate grading, during the construction process, if the material itself is not properly graded, the coarse aggregate is too large and the aggregate size is inappropriate, the needle like particle content in the crushed stone material is too high, and the actual sand rate used in the production process is less than the sand rate provided by the laboratory, the fine aggregate is not enough to fill the gaps between the coarse aggregates, resulting in the aggregate not being dense and forming free voids, providing a breeding ground for the generation of bubbles.

When testing concrete in the laboratory, the cement dosage is mainly considered for strength. If the amount of cement is increased and the amount of water is reduced while meeting the strength of the concrete, the bubbles will decrease. The reason is that excess cement slurry can fill the gaps caused by unreasonable aggregate gradation or other reasons, while the reduction of water can reduce the bubbles formed by free water (after the water bubbles in the concrete evaporate and dry, they become bubbles).